Flame retardants alter thyroid function in fish.

Feb 02, 2009

Lema, SC, JT Dickey, IR Schultz and P Swanson. 2008. Dietary exposure to 2,2´,4,4´-tetrabromodiphenyl ether (PBDE 47) alters thyroid status and thyroid hormone-regulated gene transcription in the pituitary and brain. Environmental Health Perspectives 116:1694–1699.

Synopsis by Heather Hamlin

When fed to fish, a common flame retardant affected thyroid-related gene actions and hormone levels that could alter metabolism, although the changes differed between the high and low doses tested.

Determining how these changes translate into health consequences for humans becomes a critical point since minnows and humans have similar thyroid hormone systems. In both, the thyroid gland, pituitary gland and hypothalamus work together to control many body functions, mainly metabolism. 

The findings imply that thyroid responses to PBDEs are complex and extensive, affecting thyroid actions in the brain and throughout the thyroid system. The effects differed between the high and low concentrations tested and provide another example of low dose effects of environmental chemicals.

Polybrominated diphenyl ethers (PBDEs) are flame retardants that are commonly added to plastics, foam, paints and fabrics. PBDE levels are rising in both humans and wildlife. Prior studies show the chemical alters thyroid hormones in rats, mice and fish.

North Americans have higher measured concentrations than Europeans. More studies are needed to identify the main sources of exposure for people, but at this time, dust and food head the list of possible sources. 

The adult fathead minnows were fed either 2.4 micrograms/day or 12.2 micrograms/day of PBDE for 21 days.

The amounts fed to the fish and those found in their tissues during the study are significantly higher than levels of PBDEs measured in people to date. Even though, the data provide more information about how the chemicals affect mammals.

The higher concentration significantly reduced thyroid hormone levels in the fish. Males exposed to the higher dose had reduced sperm count.

The lower concentration triggered an important gene that helps control the amount of thyroid hormone made. The gene's actions, though, were unchanged at the higher concentration.